The present invention relates to an image recording apparatus capable of forming images freely on opposite sides a paper sheet and, more particularly, to an image recording apparatus applicable to a laser printer, digital copier, etc.
There has been known an electrophotographic copier of the type having a single photoconductive drum and forming a toner image on the drum, transferring the toner image to a paper sheet, fixing it on the paper sheet, and stacking such paper sheets or copiers in a predetermined position. In this type of copier, paper sheets to which toner images have been transferred from the above in the image transfer process are always stacked face up, while paper sheets to which toner images have been transferred from the below are stacked face down without exception. This obstructs efficient arrangement of pages and cannot meet user's various needs. Some approaches have heretofore been proposed to cope with such a situation, as disclosed in Japanese Patent Laid-Open Publication (Kokai) No. 57-63559 and Japanese Utility Model Laid-Open Publication (Kokai) No. 58-166650 by way of example. One of the prior art approaches is to locate means for turning over a paper sheet on a paper transport path. Another prior art approach is to dispose two photoconductive drums face to face and transfer toner images to opposite sides of a paper sheet when the latter is moved through between the two drums.
A problem with the turn-over scheme stated above is that an extra period of time is needed to turn over paper sheets one by one, resulting in low copy productivity. Further, since a two-sided copy is moved back and forth two times through a fixing station, the copy is apt to suffer from various undesirable occurrences ascribable to thermal contraction, e.g., deviation of images, creasing and folding. On the other hand, the two drum scheme is capable of effecting side-free copying without the need for extra reversing means. Nevertheless, the two drums and their associated developing means and other various means render the overall construction of the recording apparatus bulky and complicated.